At the present time, the window regulator systems for vehicles can be divided into three large groups:                Cable window regulators which can be single rail and dual rail.        Cord-drawn window regulators.        Single- or double-arm window regulators.        
The present invention relates to window regulators of the cable type, for which reason hereinafter reference will only be made to this window regulator system.
The cable window regulator systems employed habitually, are constituted by a metallic rail on which a carriage slides which is joined to or simply pushes the window of the vehicle. The sliding of the carriage, in one direction or the other, causes the window to move upwards or downwards.
For the displacement of the carriage a cable is used which, passing through some pulley wheels mounted on the ends of the rail, is extended to the position that is occupied by the drive mechanism by means of the corresponding crank or to the electric drive motor.
In the case of manual operation, the cable is tensioned in a permanent way by means of a device termed “Bowden” which is arranged surrounding the cable, between the rail and the drum casing on which the operating crank is mounted.
In the systems of window regulators employed habitually, the rail is constituted by a metallic section obtained by cold forming, usually stamping or rolling, on which are mounted, to a great extent in a manual way, the remaining components, that is, the pulley wheels which facilitate the sliding of the traction cable, the coupling supports for the Bowden system, the elements for guiding the cable, as well as the supporting elements for the motor, when the driving action is electric. These assembly operations increase the end product cost considerably, and also involve greater complexity in operations of storage and administration of the various elements, and they imply a failure hazard both in manipulation during the assembly operations and during the working life of the product.
Also, to fasten the window regulators to the door of the vehicle, some supports are used which are joined, generally by welding, to the rail of the window regulators and through which the assembly is screwed to the door.
So, the assembly of the window regulators implies the screwing and welding of pieces of different materials and characteristics, which complicates the assembly operations of the system in the automobile.
Moreover, the geometries of vehicle windows are increasingly complicated, in such a way that the rail has to have an appropriate geometry so that the carriage can follow the movement of the window which, with the complex forms presently used, is not a straight-line movement within a same plane but rather it is approximately a helical movement.
For this reason, the rail ought to have a slight curvature but, by being constituted by a stamped metallic section, it proves very difficult to manage that the latter has the curvature with a precise permanent deformation since, these slight deformations are elastic and the section tends to recover its initial form, once the process of shaping the same has concluded. For this purpose, the rail of the window regulators is mounted on the door in a forced manner to compel it to remain bent and acquire the desired degree of curvature, which operation has to be carried out by a specialized worker since the manner of fastening the rail on the door is that which has to produce the twisting of the rail and, in consequence, the required curvature so that the carriage can follow the movement which the window glass requires.
In an attempt to resolve this problem, in the patent PCT ES99/00246 of the same applicant, a system is disclosed in which the rail of the window regulator is obtained by injection of plastic, being integrated in the rail itself some of the elements, like for example, the elements for rerouting the cable or the supports for securing to the door of the vehicle. In this patent, a casing which houses the motor is also implemented in plastic and which is mounted on the rail, by means of a system of pre-tensioning the drive cable.
In this patent the assembly operations are decreased in part and even, by being constituted in plastic but, it continues presenting a series of drawbacks like for example the following:                It is necessary to mount some metallic inserts to perform the fastening of the rail to the door of the vehicle since the securing screws cannot be threaded directly into a plastic element.        Due to the poor rigidity of the plastic, designs are required with a large surface and generally provided with a large number of stiffening ribs which implies a machine for injection of greater capacity and complexity and a large consumption of plastic.        This also implies that the space occupied by the rail produces interference with other components of the door and with those of the window regulator itself, like the cable, resulting in problems of assembly, noise, added friction and wear, lack of accessibility, etc.        The mechanical properties of the plastic are greatly influenced by the temperature, for which it can suffer deformations that shorten its useful life.        
It is mentioned that any one of the systems habitually employed, both with a metallic rail or a plastic rail have the drawback that they are made specially adapted to their utility, that is, by varying the number and typology of the pieces to be mounted it is possible to produce a different rail if the window regulator is manual or electric and also if the window regulator is single or dual rail, as a function of the different versions to be manufactured, for which reason different references must be handled which increase costs and warehouse requirements.